In your backoffice settings, when you upload a new product, you will notice a setting that you can turn on/off called "enable selling when out of stock".
If you would like to uncheck this in bulk for all your products or for some products only, here's how to do that in a few quick steps (or watch the 25 sec. video):
- go in your backoffice
- go to inventory
- select all products you'd like to stop the "selling when out of stock"
- from the "items selected" box - click on "edit selected variants"
- check the boxes for "Continue selling when out of stock" and "Are all the values the same?"
- on the next screen, leave it unchecked
- click "update"
Now you will not get orders for products that are out of stock. If you'd like to enable that setting again, follow the same steps as above and check the box for "Continue selling when product out of stock".